A PORTRAIT OF THE TAMPA BAY ESTUARY

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AMERICAN OYSTER

Bellying up to the bar takes on a different meaning when you're talking about a young American oyster looking for a place to call home. The juvenile oysters, known as "spat," can't just float along in the waters of Tampa Bay. They need a solid place to attach and grow.

That's where oyster bars come in. The spat settle in, secreting calcium carbonate to form a shell. As more and more oysters wind up in one spot, oyster bars or reefs form, stabilizing sediment at the bottom of the bay, and forming a popular spot for fish and other sea creatures to gather.

American or Eastern oysters, formally called Crassostrea virginica, are known as bivalves because they are made up of two shells that are hinged at one end. The thick, lower valve sticks to a hard surface, while the top valve is usually smaller and flatter.

The bivalves, with their grayish white, irregularly shaped shells, are a key to the health of Tampa Bay, filtering water as they feed. Oysters draw in food through the beating of small, hair-like cilia on the gills, while non-edible material is expelled.

A single oyster can filter up to 10 gallons of seawater per hour, removing sediment and algae. So the more oysters there are that call Tampa Bay home, the cleaner the waters of the bay.

American oysters were once a thriving commodity from Tampa Bay waters. The bay's oysters were shipped as far away as New York in the early 1900s, and were said to be among the most delicious anywhere.. During the mid-1960s, around 100,000 pounds of oysters were harvested in Pinellas County, with 40,000 pounds more coming from Hillsborough County. But declining water quality from dredging activities and unchecked sewage contaminated bay oysters and made them unsafe for human consumption. Today, despite dramatic improvements in water quality, oyster harvesting is still prohibited because of concerns about bacterial contamination. The good news is that oyster populations appear to be on the rise.

Oysters spawn in late winter through spring, and exemplify the true meaning of sex change, as they develop as males and typically transform into females later in life.

The oysters of Tampa Bay are most prevalent near the mouths of rivers and in sections of the bay that receive a steady supply of fresh water. Once they attach to a certain location, they remain there their entire lives.

Environmental organizations also are working to help them along. Tampa Bay Watch, for example, runs the Community Oyster Reef Enhancement program. Each year, volunteers work to create new oyster bars in the bay, comprised of old oyster shells packed together in buckets or bags and formed into reefs. They also use marine-friendly concrete to create oyster domes, which serve a similar purpose.

Creating oyster bars and domes give spat a new place to perch, and provide hiding places for smaller species of fish and crabs. At the same time, oysters serve as a food source for birds, fish and other wildlife. And the reefs draw popular gamefish such as red drum and sheepshead, making them a popular spot for local anglers.